The cannabis plant’s water and nutrient intake changes during vegetative growth. Transpiration is carried on at a rapid rate, requiring more water and nutrients. Higher levels of nitrogen are needed along with a balanced supply of potassium, phosphorous, calcium, magnesium, sulfur, and trace elements, which get used at an increased rate. The larger the plant becomes, the bigger the root system, and the faster the soil will dry out. The key to strong vegetative growth is supplying the roots with the perfect environment for strong growth and one that will discourage pests like fungus gnats that can cause a lot of damage to the fine root hairs that are essential for transferring water and nutrients from the soil up into the plant.
Vegetative growth is maintained with 16 or more hours of light. Since cannabis is photoperiod reactive, vegetative growth and flowering can be controlled by managing how many hours of light and dark the plants receive. This allows indoor horticulturists to control exactly when to initiate a flowering cycle.